Combat identification (or CID) is referred to as the process of attaining an accurate characterization of targeted and detected objects in a battlespace. Depending upon the situation, such a characterization may be limited to identification of an object with an identifier such as “friend,” “enemy,” or “unknown.” In other combat or non-combat situations, other characterizations, such as class, type, nationality, and mission configuration may be used along with appropriate identifiers. Such identification processes are sometimes carried out via combat identification systems at millimeter wave (mmW) frequencies (Ka band) and typically use an interrogator antenna system which includes a directive antenna made up of an array of antenna elements. Such interrogator array antenna systems are relatively large and heavy and therefore are not generally suitable for use on relatively light weaponry or equipment such as those which may be carried by a soldier, a hiker, or the like. As a result, these combat identification systems are typically deployed on large equipment, such as tanks and other large vehicular weapons platforms that can support this rather large and heavy equipment.
One way to reduce the size and weight of the interrogator antenna is to reduce the number of antenna elements which make up the directive antenna array. The problem with this approach is that by reducing the number of antenna elements in an array, the electrical aperture dimensions of the array antenna are correspondingly reduced in size. This in turn, leads to larger azimuth discrimination angles which undermine specific object targeting.
Moreover, since ID antenna systems require high directivity and gain, the beam forming electronic circuitry required by these types of ID antenna systems makes them inefficient due to signal losses incurred by the time phased differences necessary for the several linear radiating elements of such arrays. Horn antennas generally have high directivity and gain. However, horn antennas, configured in a small antenna system, are susceptible to a number of unwanted grating lobes in the antenna wave patterns which is reduced when compared with the number of grating lobes that would result from use of linear antenna element arrays. Canting the sectored horns used to generate both the sum and difference patterns further suppresses grating lobes.
Accordingly, there is a need for a small and light interrogator antenna with minimum or no side-lobes that can extend CID capability to the dismounted soldier or individual.